Radio communication scheme

ABSTRACT

This is a radio communication system having a radio base station controller  20  which is connected to a plurality of base stations  10   n− 1,  10   n  and  10   n +1, and then assigns a fixed channel to each of radio mobile stations  18   a,    18   b  and  18   c,  and further controls the beam patterns of the radio base stations  10   n −1,  10   n  and  10   n +1, and accordingly carries out the radio communications with the radio mobile stations  18   a,    18   b  and  18   c.  The radio base station controller  20,  when transmitting to and receiving from the different radio mobile stations  18   a,    18   b  and  18   c  to which the same channel is assigned, controls the beam patterns so that the channels do not interfere with each other.

CROSS REFERENCE TO THE RELATED APPLICATION

[0001] The subject application is related to subject matter disclosed inthe Japanese Patent Application No. Heill-356632 filed in Dec. 15, 1999in Japan, to which the subject application claims priority under theParis Convention and which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a radio communication system, aradio communication method, a radio base station controller and a radiomobile station which are used in a mobile communication service and thelike. More particularly, the present invention relates to a techniquefor keeping a communication even if a radio mobile station is moved in aradio communication system, namely, a hand-over technique.

[0004] 2. Description of the Related Art

[0005]FIG. 1 shows an example of a radio communication system in which aplurality of base stations are connected to a mobile services switchingcenter. As shown in FIG. 1, a territory (service area) to which a mobilecommunication network 200 gives a service is divided into radio zones204 referred to as cells by a number of base stations (BS) 202 andcovered by them. Several base stations 202 are bundled by a mobileservices switching center (MSC) 206, and managed and controlled by eachmobile services switching center 206. A mobile station (MS) 208 carriesout a radio communication with any of many base stations 202, andswitches a base station 202 of a communication partner, in conjunctionwith its movement. Also, a gateway mobile services switching center(G-MSC) 210 functions as a relay point when the mobile communicationnetwork 200 is mutually connected to another fixed network 212. Themobile communication network 200 is connected through the gateway mobileservices switching center 210 to another fixed network 212.

[0006] Here, when the mobile station 208 crosses one cell 204 during acommunication, the continuation of the communication with the basestation 202 requires a switching of a communication line, namely, ahand-over process for changing the base station 202 connected to themobile station 208. In the system shown in FIG. 1, the hand-over processis carried out in accordance with a control signal (for example, amessage for a hand-over) outputted to the mobile services switchingcenter 206 through the base station 202 during the connection from themobile station 208.

[0007] However, if a radius of a cell covered by each base station 202is small, a switching opportunity of a communication line is frequentlydone, which requires a very complex process. Especially, in a case ofAHS (Advanced cruise-assist Highway System) remarked as one ofIntelligent Transport Systems (ITS), a radius of a cell is very smallsuch as 50 m to 100 m at most. Thus, the switching frequency of thecommunication line of the mobile station 208 becomes very high. Inshort, a period while a car moving at a high speed stays within one cellis very short so that the hand-over process must be frequently done. Ifthe conventional hand-over technique is applied to such AHS, a rate ofthe hand-over process occupying the communication process becomes verylarge. This results in a problem that a communication efficiency becomesvery poor.

[0008] Moreover, the AHS is a system for assisting an automatic run of acar. Thus, a high reliability is required of the AHS. Hence, thecontinuation of a communication at a time of a movement between cells isan essential function in the AHS. So, a failure of the hand-over is notpermitted. However, the conventional hand-over technique does not insurethe reservation of a communication line in a hand-over destination,namely, a movement destination. In short, if the communication lines atthe hand-over destination are all used, a car during a communication cannot carry out the hand-over. This results in a problem that thecommunication with the base station is interrupted.

[0009] As mentioned above, the frequency of the hand-over processbecomes very high in the radio communication system, such as the AHS orthe like, in which an area (cell) covered by one base station is narrowand a fast mobile body is targeted. Thus, the conventional hand-overtechnique has the problems of a deterioration in a communicationefficiency and a low reliability of a communication.

SUMMARY OF THE INVENTION

[0010] The present invention is proposed in view of the above mentionedcircumstances. It is therefore an object of the present invention toprovide a radio base station controller and a radio mobile station whichcan simplify a control of a hand-over process and improve acommunication efficiency and attain a high reliability of acommunication, and a radio communication system and a radiocommunication method which use them.

[0011] In order to attain the above-mentioned objects, the first featureof the present invention lies in a radio communication systemcomprising: at least one mobile station; a plurality of base stationsconfigured to generate a plurality of beam patterns; and a base stationcontroller which is connected to the plurality of base stations, andthen assigns a fixed channel to each mobile station, controls the beampatterns of the base stations and accordingly carries out a radiocommunication with the mobile station, the base station controllerhaving a device which when carrying out a transmission and a receptionto and from a different mobile station to which the same channel isassigned, controls the beam patterns so that the channels do notinterfere with each other.

[0012] According to this first invention, one base station controllercontrols the beam pattern of any of the plurality of managed basestations, and directly carries out the radio communication with themobile station through the radio base station. That is, a signal to betransmitted to the radio mobile station is modulated within the radiobase station controller, and transmitted through the radio base stationto the radio mobile station. On the other hand, a signal transmittedfrom the radio mobile station is received through the radio basestation, and its signal is demodulated within the radio base stationcontroller. Then, the radio base station controller further assigns afixed channel (radio channel) to each of the radio mobile stations, anddoes not change its channel within the managed area, as a rule. Inshort, the base station controller controls the modulation/demodulationof the transmission/reception signal, and the beam pattern of each ofthe radio base stations, and assigns a fixed radio channel to each ofthe radio mobile stations between the managing radio base stations.Thus, the radio base station controller can control the hand-overprocess of the radio mobile station between the radio base stations.Moreover, it is possible to make its control easier. Hence, it ispossible to make the hand-over process of the radio mobile stationeffective, and also possible to improve the reliability of thecommunication between the radio base station and the radio mobilestation.

[0013] The first feature of the present invention is very effective,especially when it is applied to a system in which the radio mobilestation moves at a high speed and a moving speed of the radio mobilestation is fixed. For example, it is the AHS (Advance cruise-assistHighway System) described in the prior art. In this case, the radiomobile station is a car running on a road, or a mobile mobile stationinstalled in the car. The radio base stations are arranged at a constantinterval along the road. The movement destination (hand-overdestination) of the radio mobile station can be predicted on anexpressway having many straight portions and the like. Correspondinglyto it, the hand-over process can be easily controlled, which enables thereliability of the communication to be further improved.

[0014] In the first feature of the present invention, the radio basestation controller controls the beam patterns of the respective radiobase stations, and protects the mutual interference in the same radiochannel. Thus, it can use the same radio channel in the different radiomobile stations to thereby carry out the transmission/reception. Hence,the same radio channel can be repeatedly used to thereby attain theeffective use of a frequency.

[0015] The second feature of the present invention lies in a radio basestation controller according to the radio base station controllerdescribed in the first feature, which is connected to a plurality ofbase stations configured to generate a plurality of beam patterns, andthen controls an antenna that is installed in each of the base stationsand composed of a plurality of antenna devices, and accordingly carriesout a radio communication with a mobile station. The radio base stationcontroller comprises: an antenna controller configured to control theantenna in each of the base stations; and at least onemodulating/demodulating device configured to modulate and demodulate asignal which is transmitted to and received from the mobile station.

[0016] According to this second invention, the radio base stationcontroller can control the antenna of each radio base station anddirectly carry out the radio communication with the radio mobile stationthrough each radio base station. Here, the antenna composed of theplurality of antenna devices implies an adaptive array antenna, a smartantenna or the like in which the plurality of antenna devices aremounted. So, it can generate the plurality of beam patterns, pursue andscan the moving radio mobile station. Actually, the optimal beam patterncan be generated by setting a weight for the antenna device of eachradio base station used for the transmission/reception.

[0017] As described in the first feature, when thetransmission/reception is done by using the same radio channel in thedifferent radio mobile stations, this setting of the weight can protectthe beam patterns from interfering with each other.

[0018] The third feature of the present invention also lies in a radiobase station controller according to the radio base station controllerdescribed in the first feature, which is connected to a plurality ofbase stations arranged along a road, and then controls the plurality ofbase stations, and accordingly carries out a radio communication with atleast one mobile station running on the road. So, it comprises: a deviceconfigured to assign the same channel to each mobile station of the samespeed or the same lane; a device configured to detect at least one ofthe speed and the lane of the mobile station; and a device which whenthe speed or the lane of the mobile station is changed, changes anassignment channel, in accordance with a speed or a lane after thechange.

[0019] The third feature of the present invention actually lies in thesetting example of the radio channel assigned to each radio mobilestation, as described in the first feature. Here, the same speed and thesame lane do not require that they are perfectly equal, and it is enoughthat they are substantially equal. Actually, they imply the range inwhich the mutual interference in the same radio channel, such as thepass, the pursue and the like, is not induced between the radio mobilestations (cars) running on the road.

[0020] According to the third invention, the assignment of the sameradio channel for each radio mobile station having the same moving speedand lane enables the same radio channel to be repeatedly used withoutany mutual interference. Thus, the usage efficiency of the frequency canbe improved so that the base station controller can reserve a largernumber of channels.

[0021] The fourth feature of the present invention lies in a radio basestation controller which is connected to a plurality of base stationsarranged along a road, and then controls the plurality of base stationsand accordingly carries out a radio communication with at least onemobile station running on the road. Then, in the radio base stationcontrollers, a boundary between radio base station controllers adjacentto each other is positioned in a portion in which a movement destinationof the mobile station on the road can be pointed out. Here, the boundarybetween the radio base station controllers adjacent to each otherimplies a boundary between areas covered by the respective radio basestation controllers constituted by the set of management areas of theradio base stations controlled by the respective radio base stationcontrollers.

[0022] According to the fourth invention, the hand-over destination(movement destination) of the radio mobile station between the radiobase station controllers can be pointed out to thereby make the controlof the hand-over process in the radio mobile station easier.

[0023] The fifth feature of the present invention lies in a radiocommunication system comprising: at least one mobile station having adevice configured to select, from a plurality of same reception signals,a reception signal in which a reception state is superior; a first basestation controller having a device configured to detect a start of acommunication between a predetermined first base station and a mobilestation, a device configured to request a hand-over process to themobile station, and a device configured to transfer a transmissionsignal to the mobile station to a base station controller of a hand-overdestination, in which the first base station controller is connected toa first base station group including the predetermined first basestation; and a second base station controller having a device configuredto transmit the transmission signal transferred from the first basestation controller, through a predetermined second base station to themobile station, in which the second base station controller is connectedto a second base station group including the predetermined second basestation.

[0024] According to the fifth invention, it is possible to make thehand-over process of the radio mobile station between the radio basestation controllers effective. That is, in the hand-over between theradio base station controllers, the first radio base station controllerserving as a hand-over source, when detecting a start of a communicationbetween the radio mobile station and the predetermined first radio basestation, requests the hand-over process to the radio mobile station.Then, the side of the radio mobile station starts preparing thehand-over process. The first radio base station controller furthertransfers a signal to be transmitted through the predetermined firstradio base station to the radio mobile station, to the second radio basestation controller serving as a hand-over destination of the radiomobile station. The second base station controller transmits thetransferred signal to the radio mobile station. Thus, the same signal istransmitted to the radio mobile station from both the first and secondradio base station controllers. The radio mobile station compares thereception states of the two signals, and stops receiving the signal fromthe first radio base station controller, when the reception state of thesignal from the second radio base station controller becomes superior inconjunction with the movement, and then ends the hand-over process.Hence, it is possible to smoothly switch the communication from thefirst radio base station controller of the radio mobile station to thesecond radio base station controller. Hence, it is possible to make thecontrol of the hand-over process easier.

[0025] The sixth feature of the present invention lies in a radiocommunication method at least comprising the steps of: detecting a startof a communication between a predetermined first base station connectedto a first base station controller and a mobile station running on aroad; requesting a hand-over process to the mobile station; transferringto a second base station controller, a signal to be transferred throughthe predetermined first base station to the mobile station; transmittingthe signal to the mobile station through a predetermined second basestation connected to the second base station controller; and selecting asignal in which a reception state is superior, from two signals receivedby the mobile station.

[0026] This sixth invention is a radio communication method attained bythe radio communication system described in the fifth feature. So, ithas the same effect as the fifth feature.

[0027] Other and further objects and features of the present inventionwill become obvious upon an understanding of the illustrativeembodiments about to be described in connection with the accompanyingdrawings or will be indicated in the appended claims, and variousadvantages not referred to herein will occur to one skilled in the artupon employing of the invention in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a view showing an example of a conventional radiocommunication system in which a plurality of base stations are connectedto a mobile services switching center;

[0029]FIG. 2 is a view showing a configuration of a radio communicationsystem according to a first embodiment of the present invention;

[0030]FIG. 3 is a block diagram showing an actual configuration exampleof a radio base station controller 20 and radio base stations 10 n−1, 10n in FIG. 2, in a case of a transmitting system;

[0031]FIG. 4 is a block diagram showing an actual configuration exampleof a radio base station controller 20 and radio base stations 10 n−1, 10n in FIG. 2, in a case of a receiving system;

[0032]FIG. 5 is a flowchart showing a procedure when an optimal beampattern at a time of a transmission is generated;

[0033]FIG. 6 is a flowchart showing another procedure when an optimalbeam pattern at a time of a transmission is generated

[0034]FIG. 7 is a block diagram showing an actual configuration exampleof a radio base station controller 20 and radio base stations 10 n−1, 10n+1 in FIG. 2, in a case of a transmitting system;

[0035]FIG. 8 is a block diagram showing an actual configuration of anantenna controller 64 of FIG. 7;

[0036]FIG. 9A and 9B are views explaining a first radio channel settingexample according to a second embodiment of the present invention;

[0037]FIG. 10A and 10B are views explaining a second radio channelsetting example according to the second embodiment of the presentinvention;

[0038]FIG. 11 is a view explaining a third radio channel setting exampleaccording to the second embodiment of the present invention;

[0039]FIG. 12 is a view explaining a fourth radio channel settingexample according to the second embodiment of the present invention;

[0040]FIG. 13 is a view explaining a fifth radio channel setting exampleaccording to the second embodiment of the present invention;

[0041]FIG. 14 is a view explaining a sixth radio channel setting exampleaccording to the second embodiment of the present invention

[0042]FIG. 15 is a view showing a configuration of a radio communicationsystem according to a third embodiment of the present invention;

[0043]FIG. 16 is a view showing a configuration of a radio communicationsystem according to a fourth embodiment of the present invention; and

[0044]FIG. 17 is a flowchart showing a procedure of a hand-over processaccording to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] Various embodiments of the present invention will be describedwith reference to the accompanying drawings. It is to be noted that thesame or similar reference numerals are applied to the same or similarparts and elements throughout the drawings, and the description of thesame or similar parts and elements will be omitted or simplified.

[0046] (First Embodiment)

[0047]FIG. 2 is a view showing a configuration of a radio communicationsystem according to a first embodiment of the present invention. In theradio communication system according to the first embodiment of thepresent invention, a plurality of areas (cells) covered by each basestation constitute an entire service area of a mobile communicationnetwork. In FIG. 2, the explanation is done under the assumption thatthe number of base stations managed by one base station controller is 3,for the purpose of simple explanation.

[0048] In the radio communication system according to the firstembodiment of the present invention in FIG. 2, areas (hereafter,referred to as base station areas) 12 n−1, 12 n and 12 n+1 managed byradio base stations 10 n−1, 10 n and 10 n+1 divide parts of an servicearea and covers them. The respective radio base stations 10 n−1, 10 nand 10 n+1 have antennas 14 n−1, 14 n and 14 n+1, respectively, whichcan generate a plurality of beam patterns. Each of the respective basestation areas 12 n−1, 12 n, 12 n+1 is provided with a plurality of areas(hereafter, referred to as beam areas) 16-1, 16-2 to 16-m generated bytheir antennas 14 n−1, 14 n and 14 n+1. Each of the radio base stations10 n−1, 10 n and 10 n+1 carries out a radio communication with a radiomobile station 18 (18 a, 18 b and 18 c) within each of the base stationareas 12 n−1, 12 n, 12 n+1 through each of the antennas 14 n−1, 14 n and14 n+1.

[0049] Similarly to the radio communication system of FIG. 1, the radiobase stations 10 n−1, 10 n and 10 n+1 are managed by one radio basestation controller 20. However, the present invention is different fromthe conventional configuration of FIG. 1 in that the respective radiobase stations 10 n−1, 10 n and 10 n+1 do not have a demodulator fordemodulating a signal received from the radio mobile station 18 and amodulator for modulating a signal sent to the radio mobile station 18.In short, the radio communication system according to the firstembodiment of the present invention in FIG. 2 does not carry out ademodulation at a time of a reception and a modulation at a time of atransmission, namely, it does not carry out the modulation/demodulation.It only transmits a modulated reception signal to the radio base stationcontroller 20 and only transmits a signal modulated by the radio basestation controller 20 to the radio mobile station 18. Moreover, thepresent invention has a feature that this modulation/demodulation iscarried out by the radio base station controller 20 managing the radiobase stations 10 n−1, 10 n and 10 n+1.

[0050] That is, in the first embodiment of the present invention, in acase of the receiving system (from the radio mobile station 18 to theradio base stations 10 n−1, 10 n and 10 n+1), each of the radio basestations 10 n−1, 10 n and 10 n+1, when receiving a modulated signal fromthe radio mobile station 18 within each of the base station areas 12n−1, 12 n, 12 n+1, transmits the signal to the radio base stationcontroller 20 in its original state. Then, the radio base stationcontroller 20 having a modulator/demodulator 22 demodulates themodulated signal. On the other hand, in a case of the transmittingsystem (from the radio base stations 10 n−1, 10 n and 10 n+1 to theradio mobile station 18), the modulator/demodulator 22 of the radio basestation controller 20 modulates a signal in advance. Then, the radiobase station controller 20 transmits the modulated signal through theradio base stations 10 n−1, 10 n and 10 n+1 to the radio mobile station18.

[0051] Usually, the radio base station controller 20 and the radio basestations 10 n−1, 10 n and 10 n+1 are connected through wire lines toeach other. As its connection, there is an RoF (Radio on Fiber)transmission in which a radio signal is transmitted, for example,through an optical cable. Not only various information signals but alsoa control signal through which the radio base station controller 20controls the radio base stations 10 n−1, 10 n and 10 n+1 are transmittedbetween the radio base station controller 20 and the radio base stations10 n−1, 10 n and 10 n+1. Moreover, the radio base station controller 20is connected through a network 24 to other radio base stationcontrollers 26. By the way, a plurality of radio base stations (notshown) are also connected to the other radio base station controllers 26although this is natural.

[0052]FIG. 3 is a block diagram showing the actual configuration exampleof the radio base station controller 20 and the radio base stations 10n−1, 10 n in FIG. 2. The example of FIG. 3 shows the case of thetransmitting system (from the radio base stations 10 n−1, 10 n to theradio mobile station 18). For the purpose of simple explanation, onlythe basic configuration is illustrated, and a frequency converter andthe like are omitted. As shown in FIG. 3, the radio base stationcontroller 20 is provided with: a modulator 28 for modulating atransmission signal; an antenna controller 30 for controlling theantennas 14 n−1, 14 n of the radio base stations 10 n−1, 10 n; and anE/O converter 32 (32 a, 32 b, 32 c and 32 d) for converting thetransmission signal modulated by the modulator 28 from an electricsignal into an optical signal. In FIG. 3, one modulator 28 modulates atransmission signal to be transmitted to both the radio base stations 10n−1, 10 n. However, the number of modulators 28 is not limited to it.For example, it may be designed to mount a dedicated modulator for eachmanaged radio base station.

[0053] On the other hand, the radio base station 10 n−1 is composed of:an O/E converter 34 (34 a, 34 b) for converting the transmission signalsent by the radio base station controller 20 from an optical signal intoan electric signal; and an antenna device 36 (36 a, 36 b) for emittingthe transmission signal as an electric wave. Similarly, the radio basestation 10 n is composed of: an O/E converter 38 (38 a, 38 b) for againconverting the transmission signal sent by the radio base stationcontroller 20 from the optical signal into the electric signal; and anantenna device 40 (40 a, 40 b) for emitting the transmission signal asan electric wave. The antenna devices 36, 40 are parts of a plurality ofantenna devices constituting the antennas 14 n−1, 14 n of FIG. 2. Here,they correspond to the devices for transmission. Then, the radio basestation controller 20 and the radio base stations 10 n−1, 10 n areconnected through an optical fiber 42 (42 a, 42 b, 42 c and 42 d) toeach other.

[0054] The operations of the radio base station controller 20 and theradio base stations 10 n−1, 10 n of FIG. 2 in the case of thetransmitting system will be described below with reference to FIG. 3. Atfirst, the modulator 28 of the radio base station controller 20modulates a transmission signal, and outputs through the frequencyconverter (not shown), the antenna controller 30 and the like to the E/Oconverter 32. The E/O converter 32 converts the transmission signal intoan optical frequency area, and sends through the respectively connectedoptical fiber 42 (42 a, 42 b, 42 c and 42 d) to the radio base stations10 n−1, 10 n. Then, after the O/E converters 34, 38 again convert thesent transmission signals into the electric signals and then theamplifications are performed on them, the radio base stations 10 n−1, 10n uses the antenna devices 36, 40 to then emit as the electric wave.

[0055] Here, the antenna controller 30 within the radio base stationcontroller 20 controls the antenna devices 36, 40 of the radio basestations 10 n−1, 10 n, as described below. That is, the antennacontroller 30 has a function of optimizing the beam pattern to the radiomobile station 18 by selecting a weight optimal for the settings of theantenna devices 36, 40. As an actual control method, for example, thereare settings of excitation amplifications and excitation phases of theantenna devices 36, 40. Then, the antenna controller 30 controls theantenna devices 36, 40 and scans a beam so that the beam is alwaysdirected to the moving radio mobile station 18.

[0056] For example, in FIG. 2, when the radio mobile station 18 movesfrom a position of a radio mobile station 18 a through a position of aradio mobile station 18 b to a position of a radio mobile station 18 c,the antenna controller 30 carries out a control as described below. Atfirst, while the radio mobile station 18 moves from the position of theradio mobile station 18 a to the position of the radio mobile station 18b, it uses only the antenna device 36 of the radio base station 10 n−1.The beam area 16 is sequentially switched from the beam area 16-1 to thebeam area 16-m in conjunction with the movement of the radio mobilestation 18 so that the beam is always directed to the radio mobilestation 18.

[0057] When the radio mobile station 18 tries to go from the position ofthe radio mobile station 18 b into the base station area 12 n of theradio base station 10 n, the antenna controller 30 switches the controltarget from the antenna device 36 of the radio base station 10 n−1 tothe antenna device 40 of the radio base station 10 n. Then, similarly tothe above-mentioned case, it controls the antenna device 40 andgenerates a beam pattern suitable for the radio mobile station 18.Moreover, when the radio mobile station 18 moves to the position of theradio mobile station 18 c and goes into the base station area 12 n+1 ofthe radio base station 10 n+1, the antenna controller 30 switches thecontrol target from the antenna device 40 of the radio base station 10 nto an antenna device (not shown) of the radio base station 10 n+1, andcarries out the similar control. In this way, the antenna controller 30controls the antenna devices 36, 40 of the respective radio basestations 10 n−1, 10 n and 10 n+1 and the like. Thus, the respectiveradio base stations 10 n−1, 10 n and 10 n+1 can generate the beampattern always suitable for the moving radio mobile station 18. Hence,it is possible to carry out the excellent radio communication with theradio mobile station 18.

[0058]FIG. 4 is a block diagram showing the actual configuration exampleof the radio base station controller 20 and the radio base stations 10n−1, 10 n of FIG. 2, in the case of the receiving system (from the radiomobile station 18 to the radio base stations 10 n−1, 10 n). Also, in thecase of the receiving system, the similar function can be attained underthe configuration similar to that of the transmitting system shown inFIG. 3. However, the flow of the signal is opposite. So, in thereceiving system of FIG. 4, the modulator 28 within the radio basestation controller 20 of the transmission system shown in FIG. 3 issubstituted for a demodulator 44, the E/O converter 32 is substitutedfor an O/E converter 48, and the antenna controller 30 is substitutedfor an antenna controller 46 having a configuration different from thatof the antenna controller 30, respectively. Moreover, the O/E converters34, 38 within the radio base stations 10 n−1, 10 n are substituted forE/O converters 50, 54.

[0059] The antenna controller 46 within the radio base stationcontroller 20 of FIG. 4 has a receiving signal measuring device 60 formeasuring a reception strength, a signal wave form and the like of asignal received by each of receptions antenna devices 52, 56 of theradio base stations 10 n−1, 10 n. The antenna controller 46 can optimizea beam pattern generated by the antenna device, in accordance with theresult measured by the measuring device 60. For example, it is possibleto select only the antenna devices 52, 56 having the strong receptionstrengths from the result measured by the measuring device 60 to therebyreceive only the strongest signal and not to receive the unnecessaryelectric waves (interference signals). Also, by weighting the respectiveantenna devices 52, 56, a null point (zero point) of the beam patternmay be defined in a direction in which an interference signal to beremoved is inputted. This is because the reception of the interferencewave can be removed by directing the null point to the direction of theinterference wave. Or, the antenna devices 52, 56 may be driven so thata beam having a maximum gain is directed to a direction of a desirablesignal.

[0060] In the first embodiment of the present invention, the number ofradio base stations 10 n−1, 10 n and 10 n+1 connected to the radio basestation controller 20, the number of antenna devices mounted in therespective radio base stations 10 n−1, 10 n and 10 n+1 and the like arenot limited to the configurations shown in FIGS. 2 to 4. Also, thetransmitting system and the receiving system are separately described.However, it may be naturally designed that the radio base stationcontroller 20 and the radio base stations 10 n−1, 10 n and 10 n+1 havethe configurations of both the transmitting system and the receivingsystem. In this case, the usage of a branching filter, a circulator, aswitch and the like enables the antenna devices 36, 40, 52 and 56 in therespective radio base stations to be shared in the transmitting systemand the receiving system. Moreover, the combination of the modulator 28and the demodulator 44 may be used as one modulator/demodulator.

[0061] The first embodiment of the present invention especially targetsan inter-lane communication in a high rode traffic system (hereafter,abbreviated as ITS) in a so-called mobile communication system. Here,the feature of the inter-lane communication is described. A car (radiomobile station), since usually running on a road, receives somelimitation on a moving direction of the car. In a case of an expressway,the car runs on only a straight line, and does not turn right or left,except an interchange, a service area and the like. Thus, the radio basestations targeting the ITS are arranged in a line along the road. Thisfact can be regarded as the situation that hand-over destinations of therespective radio base stations are limited, from the viewpoint of thehand-over technique in the radio communication. For example, in FIG. 2,let us suppose that the radio mobile station 18 goes from the positionof the radio mobile station 18 a through the position of the radiomobile station 18 b into the position of the radio mobile station 18 c.In short, the radio mobile station 18 moves in the passage order of thebase station areas 12 n−1, 12 n and 12 n+1. As mentioned above, in thebase station area 12 n−1, the scanning operation is carried out in theorder of the beam areas 16-1, 16-2, 16-3 to 16-m. When the presentinvention is applied to the radio system in which such beam areas 16 areconnected in series (in a line), the hand-over destinations are limitedas mentioned above. Hence, it is possible to largely simplify thecontrol of the hand-over. Thus, this has a merit of providing a radiocommunication system having a high reliability.

[0062] The operation of the first embodiment of the present inventionapplied to the ITS will be described below with reference to FIG. 2. Inthe first embodiment of the present invention, the radio base stationcontroller 20 assigns one particular radio channel, for example, to aradio mobile station 18 (in this case, a car) within the base stationarea 12 n−1 of the radio base station 10 n−1. This radio channel can beused by only the radio mobile station 18 while it stays within the basestation area 12 n−1. Typically, as a method for attaining a multipleaccess, there are a time division multiple access (TDMA), a frequencydivision multiple access (FDMA) and a code division multiple access(CDMA). For example, in a case of the TDMA, the radio channelcorresponds to a time slot. In a case of the FDMA, it corresponds to afrequency band. And, in a case of the CDMA, it corresponds to a PN(Pseudo Noise) code (diffusion code).

[0063] The radio mobile station 18 uses the assigned radio channel andsends a signal. Of course, it is the radio base station 10 n−1 thatreceives the sent signal. However, the radio base station receiving thesignal is not always limited to only the radio base station 10 n−1. Forexample, even the radio base station 10 n adjacent to the radio basestation 10 n−1 can receive it.

[0064] Tentatively let us suppose that an information signal from theradio mobile station 18 within the base station area 12 n−1 of the radiobase station 10 n−1 is received by both the radio base stations 10 n−1,10 n. In this case, the same two signals received by the respectiveradio base stations 10 n−1, 10 n are sent to the radio base stationcontroller 20. Then, the radio base station controller 20 can determinea base station area in which the radio mobile station 18 is present. Thedetermination of the base station area is carried out, for example, inthe following procedure.

[0065] (a) Measure received signal strength indicators (RSSIs) of thetwo signals.

[0066] (b) Compare the strengths of the two measured RSSIs.

[0067] (c) Determine that the radio mobile station 18 is present in abase station area of a radio base station having the strongest RSSI,from the compared result.

[0068] The radio base station controller 20, when there is aninformation to be sent to the radio mobile station 18, may send thesignal through a radio base station (for example, the radio base station10 n−1) determined as the radio base station in which the radio mobilestation 18 is present. The radio base station controller 20 carries outthe determination each time the signal is sent from the radio mobilestation 18. Until it is determined that the radio mobile station 18 ispresent in a base station area 12 n of a different radio base station(for example, the radio base station 10 n), the radio base stationcontroller 20 continues to send the signal through the radio basestation 10 n−1.

[0069] The radio base station controller 20 can select a beam patternoptimal for a radio base station at a time of a reception, on the basisof the signal sent by the radio mobile station 18. (1) For example, in acase of the configuration shown in FIG. 4, the receiving signalmeasuring device 60 within the antenna controller 46 can measure thereception strengths, the signal wave forms and the like of the radiobase stations 10 n−1, 10 n. If the reception strengths of the respectiveantenna devices 52, 56 are monitored to accordingly select the antennadevices 52, 56 having the strongest reception strength, it is possibleto select the beam pattern optimal for the radio base station. Also, (2)an adaptive array for setting an optimal weight based on a receptionsignal of each antenna device may be configured to accordingly select anoptimal beam pattern. Directing the beam to the radio mobile station 18or suppressing the interference wave enables the desirable beam patternto be selected. Or, (3) a position of the radio mobile station 18 isrecognized by using an external sensor or the like, and an optimal beamis directed to the radio mobile station 18. Accordingly, an optimal beampattern may be selected.

[0070] The radio base station controller 20 correlates the receptionbeam pattern selected by using the above-mentioned method to anidentification information of the targeted radio mobile station 18, andgenerates a beam pattern information, and then stores it in apredetermined memory. When the signal is sent to the radio mobilestation 18, the optimal transmission beam pattern can be generated byreferring to the beam pattern information of the radio mobile station18. By the way, when the transmitting method between the radio basestation controller 20 and the radio mobile station 18 is a TDD (TimeDivision Duplex) method and further a fixed slot assignment is carriedout, the beam pattern used in the reception slot can be used in itsoriginal state as the transmission beam pattern. Thus, in this case, theradio base station controller 20 does not need to hold the beam patterninformation.

[0071] As mentioned above, in the first embodiment of the presentinvention, the radio base station in which the radio mobile station 18is present is determined in accordance with the signal from the radiomobile station 18. Thus, in this embodiment, it is enough to select anoptimal reception beam pattern only for the radio base station in whichthe radio mobile station 18 is present. The radio base stationcontroller 20 generates the transmission beam pattern optimal for thecorresponding radio base station at a time of a transmission, andattains a radio communication having a high reliability. Its procedureis carried out, for example, in the following procedure. FIG. 5 is aflowchart showing the process when an optimal beam pattern is generatedat a time of a transmission.

[0072] As shown in FIG. 5, the radio base station controller 20 firstlymeasures the RSSIs of all radio base stations receiving a transmissionsignal from the radio mobile station 18 (Step S101). Next, the radiobase station controller 20 selects the maximum of the measured RSSIs. Inshort, it determines a radio base station in which the radio mobilestation 18 is present (Step S102). It selects an optimal reception beampattern of the radio base station having the selected maximum RSSI (StepS103). If there is no information to be sent to the radio mobile station18 (Step S104 NO), the operational flow again returns back to the stepS101. It measures the RSSIs of all the radio base stations receiving thetransmission signal from the radio mobile station 18.

[0073] On the other hand, if there is the information to be sent to theradio mobile station 18 (Step S104 YES), it holds the optimal receptionbeam pattern selected at the step S103 and the identificationinformation of the targeted radio mobile station 18 as the beam patterninformation (Step S105). In accordance with the beam pattern informationheld at the step S105, a transmission beam pattern to be currently sentto the radio mobile station 18 is generated by its radio base station(Step S106). After that, it sends the information signal to the radiomobile station 18 (Step S107).

[0074] As mentioned above, the first embodiment of the present inventiontargets the ITS inter-lane communication. The movement destination(hand-over destination) of the radio mobile station 18 is limited, inthis ITS inter-lane communication. Actually, as shown in the procedureof FIG. 5, it is not necessary to measure the RSSIs of all the radiobase stations receiving the transmission signal from the radio mobilestation 18 (Step S101 of FIG. 5). In short, it is possible to predictthe movement destination of the radio mobile station 18. Thus, after themaximum RSSI is once selected and the position of the radio mobilestation 18 is pointed out, it is enough that the radio base station inwhich the radio mobile station 18 is currently present and the radiobase station (the adjacent radio base station) corresponding to themovement destination is only targeted for the RSSI measurement. FIG. 6is a flowchart showing a procedure in this case.

[0075] As shown in FIG. 6, the radio base station controller 20 firstlymeasures the RSSIs of all radio base stations receiving a transmissionsignal from the radio mobile station 18 (Step S201). Next, the radiobase station controller 20 selects the maximum of the measured RSSIs,and determines a radio base station in which the radio mobile station 18is present (Step S202). It selects an optimal reception beam pattern ofthe radio base station having the selected maximum RSSI (Step S203). Ifthere is no information to be sent to the radio mobile station 18 (StepS204 NO), at this time, it measures the RSSI of the transmission signalof the radio mobile station 18, for the radio base station pointed outat the step S202 and the radio base station adjacent to it (Step S205).Then, the operational flow returns back to the step S202.

[0076] On the other hand, if there is the information to be sent to theradio mobile station 18 (Step S204 YES), it holds the optimal receptionbeam pattern selected at the step S203 and the identificationinformation of the targeted radio mobile station 18 as the beam patterninformation (Step S206). In accordance with the beam pattern informationheld at the step S206, a transmission beam pattern to the radio mobilestation 18 is generated by its radio base station, at this time (StepS207). After that, it sends the information signal to the radio mobilestation 18 (Step S208). This case can relax the treatment load on theradio base station controller 20 to accordingly reduce the entiretreatment time.

[0077] In the first embodiment of the present invention, the same radiochannel is assigned to a plurality of radio mobile stations within thearea of the same radio base station, in order to effectively use afrequency. For this reason, it is necessary that the information whichare sent and received between the respective radio base stations do notinterfere with each other. The case that the same radio channel isassigned to the radio mobile station 18 a existing in the base stationarea 12 n−1 of the radio base station 10 n−1 and the radio mobilestation 18 c existing in the base station area 12 n+1 of the radio basestation 10 n+1 will be described below with reference to FIG. 2. FIG. 7is a block diagram showing the actual configuration example of the radiobase station controller 20 and the radio base stations 10 n−1, 10 n+1 ofFIG. 2, in the above case. FIG. 7 shows the case of the transmittingsystem, similarly to FIG. 3. For the purpose of simple illustration,only the basic configuration is illustrated, and the frequency converterand the like are omitted.

[0078] As shown in FIG. 7, the radio base station controller 20 isprovided with: a modulator 62 (62 a, 62 b) for modulating a signal; anantenna controller 64 for controlling the antennas 14 n−1, 14 n+1 of theradio base stations 10 n−1, 10 n+1; and an E/O converter 66 (66 a, 66 b,66 c and 66 d) for converting the signal modulated by the modulator 62from an electric signal into an optical signal. Here, the modulators 62a, 62 b are operated at the same radio channel in a case of a frequencyshare (if the same frequency is used).

[0079] On the other hand, the radio base station 10 n−1 is composed of:an O/E converter 68 (68 a, 68 b) for again converting the transmissionsignal sent by the radio base station controller 20 from an opticalsignal into an electrical signal; and an antenna device 70 (70 a, 70 b)for emitting the transmission signal as an electric wave. The radio basestation 10 n+1 is composed of: an O/E converter 72 (72 a, 72 b) foragain converting the transmission signal sent by the radio base stationcontroller 20 from the optical signal into the electric signal; and anantenna device 74 (74 a, 74 b) for emitting the transmission signal asan electric wave. The antenna devices 70, 74 are parts of a plurality ofantenna devices constituting the antennas 14 n−1, 14 n+1 of FIG. 2.Here, they correspond to the devices for transmission. Then, the radiobase station controller 20 and the radio base stations 10 n−1, 10 n+1are connected through an optical fiber 76 (76 a, 76 b, 76 c and 76 d) toeach other.

[0080] The operations of the radio base station controller 20 and theradio base stations 10 n−1, 10 n+1 of FIG. 2 will be described belowwith reference to FIG. 7. The modulator 62 modulates a transmissionsignal and outputs to the antenna controller 64. The antenna controller64 selects the antenna devices 70, 74 to be used for a transmission ofthe transmission signal. Moreover, it sets the predetermined weights forthe transmission signals corresponding to the selected antenna devices70, 74. This weighting prevents a beam pattern generated by the antennadevice 70 and a beam pattern generated by the antenna device 74 frominterfering with each other.

[0081] For example, the antenna device 70 of the radio base station 10n−1 is selected for a transmission signal from the modulator 62 a, and apredetermined weight is set for the transmission signal. Thetransmission signal weighted by the antenna controller 64 is emittedthrough the E/O converters 66 a, 66 b, the optical fibers 76 a, 76 b andthe O/E converter 68 from the antenna device 70. Similarly, the antennadevice 74 of the radio base station 10 n+1 is selected for atransmission signal from the modulator 62 b, and a transmission signalfor which a predetermined weight is set is emitted from the antennadevice 74. The weightings of the respective antenna devices 70, 74prevent the beam pattern of the antenna device 70 and the beam patternof the antenna device 74 from interfering with each other. For thisreason, even if the same radio channel is shared between the radio basestations 10 n−1 10 n+1, this sharing has no influence on thecommunication line.

[0082]FIG. 8 is a block diagram showing the actual configuration of theantenna controller 64 of FIG. 7. As shown in FIG. 8, the antennacontroller 64 is composed of an allotter 78 (78 a, 78 b) fordistributing the transmission signal from the modulator 62, a weightingdevice 80 (80 a, 80 b, 80 c and 80 d) for setting a predetermined weightfor the transmission signal, a matrix switch 82 (82 a, 82 b) forselecting the antenna devices 70, 74 used for transmission, and asynthesizer 84 (84 a, 84 b, 84 c and 84 d) for synthesizing thedistributed transmission signals. The allotter 78 firstly distributesthe transmission signal from the modulator 62, by a number correspondingto the number of antenna devices used by the respective radio basestations 10 n−1, 10 n+1 in the transmission. Here, each of the radiobase stations 10 n−1, 10 n+1 has two antenna devices 70, 74. Thus, thesame two transmission signals are generated. The predetermined weight isset for the distributed transmission signals by each weighting device80. The weighted transmission signal is outputted to the matrix switch82. The matrix switch 82 has a plurality of output ports correspondingto the respective antenna devices 70, 74, and selects the antennadevices 70, 74 used for the transmission, and then outputs thetransmission signal to the synthesizer 84 corresponding to each of theantenna devices 70, 74. The synthesizer 84 synthesizes the signals fromboth the matrix switches 82 a, 82 b. Then, an output signal of thesynthesizer 84 is outputted to the respectively corresponding antennadevices 70, 74. By the way, in FIG. 8, one of the antenna devices 70, 74is shared in the transmission signals from the two modulators 62 a, 62b. Thus, the synthesizer 84 is required. If one of the antenna devices70, 74 is not shared in the transmission signals from the plurality ofmodulators 62, a switch may be used instead of the synthesizer.

[0083] Due to the above-mentioned configuration, the antenna controller64 can select the predetermined antenna devices 70, 74 and set thepredetermined weight for the selected antenna devices 70, 74. Thus, itis possible to prevent the beam pattern generated by the antenna device70 and the beam pattern generated by the antenna device 74 frominterfering with each other. So, the same radio channel can be used.That is, the same channel can be repeatedly used within the area coveredby one radio base station controller 20. Hence, this is very effectivefrom the viewpoint of the effective utilization of the limited frequencyresource.

[0084] If the transmission signal is a digital signal in FIG. 7, most ofthe configuration of the antenna controller 64 can be attained by usinga software, differently from the configuration of FIG. 8. For example,it can be attained by using DSP (Digital Signal Processor). In thiscase, the configuration and the control can be easily changed byre-writing the software. Thus, this has the merit that the flexibilitywith regard to a change or a version-up of the system is high. This caserequires that the signal from the antenna controller 64 is convertedfrom a digital signal to an analog signal by using a D/A converter orthe like.

[0085] As mentioned above, if the same radio channel is assigned to aplurality of radio mobile stations within the area of the same radiobase station controller, there may be a case that the radio base stationcontroller receives a transmission signal from a different radio mobilestation in the same channel. In this case, as a method for selecting oneradio base station suitable for each radio mobile station, there are thefollowing two methods:

[0086] (1) a method for selecting radio base stations suitable for eachradio mobile station serving as a candidate in advance and selecting aradio base station having a maximum RSSI among them; and

[0087] (2) a method for demodulating respective reception signals fromthe respective radio base stations, and using the information such as adestination address of its packet, a transmission source address and thelike, and then judging whether or not they are the same packet.

[0088] In this method (2), if they are judged as the same packet, it isenough to select as the suitable radio base station, the radio basestation having the maximum RSSI from the received radio base stations.Accordingly, while the radio mobile station moves within the same radiobase station controller, it is possible to switch the radio base stationwithout sending and receiving a message such as a hand-over request andthe like. Also, the same radio channel is assigned to all the radio basestations managed by the radio base station controller. Thus, when thehand-over is carried out between those radio base stations, adisconnection of a call caused by a lack of a band at the hand-overdestination and the like is never induced. Hence, a seamlesscommunication can be done.

[0089] As mentioned above, according to the first embodiment of thepresent invention, the radio base station controller can carry out thehand-over control and the beam control between the radio base stations.Moreover, the hand-over destination between the radio base stations areuniquely determined. Thus, the hand-over between the radio base stationscan be attained by using the easy control.

[0090] The first embodiment of the present invention is applied to atwo-way communication. However, the present invention can be applied to,for example, a communication of only an up-link. In this case, themodulator and the like are not necessary since the radio base stationcontroller has only a receiving device. Moreover, with regard to thechannel assignment, only the channel for the up-link may be assigned.

[0091] (Second Embodiment)

[0092] A second embodiment of the present invention will be describedbelow. In this second embodiment, a setting example of a radio channelin the first embodiment of the present invention is explained by usingfive examples.

[0093] (First Radio Channel Setting Example)

[0094]FIG. 9 is a view explaining a first radio channel setting exampleaccording to the second embodiment of the present invention. In FIG. 9,the explanation is done under the assumption that the number of radiobase stations managed by one radio base station controller is 5, for thepurpose of simple explanation. Also, it is assumed that the number ofradio channels which can be used within one base station controller is3.

[0095] In a radio communication system shown in FIG. 9, a radio basestation controller 86 manages five radio base stations 88 (88 a, 88 b,88 c, 88 d and 88 e) and carries out the respective controls. Those fiveradio base stations 88 are installed for each approximately “r” intervalalong a road 90 (90 a, 90 b). Each of the radio base stations 88 has anantenna 92 (92 a, 92 b, 92 c, 92 d and 92 e). Then, the each radio basestation 88 carry out a radio communication with a radio mobile station94 (94 a, 94 b, 94 c, 94 d and 94 e) within a base station area (notshown) constituted by a beam pattern of the antenna 92, by using apredetermined radio channel. Here, each antenna 92 is an antenna havingone or more beam patterns or having a variable beam pattern shape. Forexample, it may be constituted by an array antenna composed of aplurality of antenna devices.

[0096] The first radio channel setting example is carried out by thefollowing procedure.

[0097] (a) The radio base station controller 86 detects a speed of theradio mobile station 94 moving on the road 90, through each of the radiobase stations 88. As a method for detecting this speed of the radiomobile station 94, there may be a method for detecting from a sensor (anelectric wave sensor, an optical sensor and the like) of the radio basestation 88, a method in which a mobile body itself installed in theradio mobile station 94 measures its speed by using a speed meter andthen its measured result is reported to the radio base station 88, andthe like.

[0098] (b) The speeds of the radio mobile stations 94 are grouped inaccordance with the sensed speeds of the radio mobile stations 94. Thisgrouping is done depending on the number of radio channels which theradio base station controller 86 can use. In FIG. 9, the radio mobilestations 94 a, 94 b and 94 e move at a speed v1 (=80 km/h), the radiomobile station 94 c moves at a speed v2 (=100 km/h) and the radio mobilestation 94 d moves at a speed v3 (=120 km/h) on the road 90 in the samedirection. For this reason, the grouping is set, for example, such as agroup 1 of the speed v1, a group 2 of the speed v2 and a group 3 of thespeed v3.

[0099] (c) The radio channel is assigned for each set group. FIG. 9Bshows an example of the assignment. In FIG. 9B, a channel ch1 isassigned to the group 1 (the speed v1), a channel ch2 is assigned to thegroup 2 (the speed v2 ) and a channel ch3 is assigned to the group 3(the speed v3), respectively.

[0100] In this first radio channel setting example, the grouping is donefor each radio mobile station 94 having the same speed. A differentradio channel is assigned to each group. Accordingly, this prevents thebeam patterns using the same channel from intersecting with each other(interfering with each other). Actually, in FIG. 9A, a pass or a pursuitdoes not occur between the radio mobile stations 94 a, 94 b and 94 e ofthe same speed (the same average speed). Thus, as shown in FIG. 9B, thesame radio channel ch1 is assigned to those radio mobile stations 94 a,94 b and 94 e so as to avoid the interference in the same radio channelch1. Hence, the radio channel ch1 can be repeatedly used.

[0101] That is, according to this first radio channel setting example,it is possible to improve the usage efficiency of the frequency andthereby reserve a larger number of radio channels. Also, this iseffective for a Platoon run that is a car group run in which a distancebetween the cars is short.

[0102] (Second Radio Channel Setting Example)

[0103] A second radio channel setting example according to the secondembodiment of the present invention will be described below. FIG. 10A isa view explaining this second setting example. The equal or similarsymbols are given to the portions equal or similar to those of FIGS. 9Aand 9B.

[0104] The grouping in the first radio channel setting example is donein accordance with the moving speed of the radio mobile station.However, in this second radio channel setting example, the grouping isdone in accordance with a running lane of the radio mobile station. Itis assumed in FIG. 10A that the radio mobile stations running on thesame lane have the same speed.

[0105] The second radio channel setting example is carried out in thefollowing procedure.

[0106] (a) The radio base station controller 86 detects a running laneof a radio mobile station 98, through each of the radio base stations88. As a method for detecting this running lane of the radio mobilestation 98, there may be a method for detecting from the sensor (theelectric wave sensor, the optical sensor and the like) of the radio basestation 88, a method for measuring a position of a mobile body itselfthrough a sensor mounted in the mobile body itself installed in theradio mobile station 98 and then sending this information to the radiobase station 88, and the like.

[0107] (b) The running lanes of the radio mobile stations 98 are groupedin accordance with the sensed running lanes of the radio mobile stations98. This grouping is done depending on the number of radio channelswhich the radio base station controller 86 can use. As shown in FIG.10A, the radio mobile stations 98 a, 98 b move on a lane 96 a, the radiomobile stations 98 c, 98 d move on a lane 96 b and the radio mobilestation 98 e moves on a lane 96 c in the same direction. For thisreason, the grouping is set, for example, such as a group 1 of the lane96 a, a group 2 of the lane 96 b and a group 3 of the lane 96 c.

[0108] (c) The radio channel is assigned for each set group. FIG. 10Bshows an example of the assignment. In FIG. 10B, a channel ch4 isassigned to the group 1 (the lane 96 a), a channel ch5 is assigned tothe group 2 (the lane 96 b) and a channel ch6 is assigned to the group 3(the lane 96 c), respectively.

[0109] In this second radio channel setting example, the grouping isdone for each radio mobile stations 98 running on the same lane. Adifferent radio channel is assigned to each group. Accordingly, thisprevents the beam patterns using the same channel from intersecting witheach other (interfering with each other). Actually, as shown in FIG.10B, the pass or the pursuit does not occur between the radio mobilestations 98 running on the different lanes. Thus, the same radio channelis assigned to each radio mobile stations 98 running on the same lane soas to avoid the interference in the same radio channel. Hence, the sameradio channel can be repeatedly used.

[0110] That is, according to this second radio channel setting example,it is possible to improve the usage efficiency of the frequency andthereby reserve a larger number of radio channels. Also, this iseffective for the Platoon run that is the car group run in which thedistance between the cars is short

[0111] Moreover, in this second radio channel setting example, if adistance between two different lanes is separated by a distance underwhich the radio channels used by the respective lanes do not interferewith each other, it is possible to further carry out a re-use of thesame radio channel. For example, in FIG. 10B, the lane 96 a and the lane96 c are spatially separated by a distance corresponding to a width ofone lane (the lane 96 b). Thus, if the channel ch4 and the channel ch6have the same channel, the number of channels can be reduced from 4 to2. Hence, it is possible to further improve the usage efficiency of thefrequency.

[0112] (Third Radio Channel Setting Example)

[0113] A third radio channel setting example according to the secondembodiment of the present invention will be described below. FIG. 11 isa view explaining this third radio channel setting example. The equal orsimilar symbols are given to the portions equal or similar to those ofFIGS. 9A and 9B. This third setting example is applied to a case thatthe speed of the radio mobile station is changed, in the first andsecond setting examples. Here, let us suppose that the number ofavailable radio channels is 2, and the grouping is done for eachdifferent two movement speeds of the radio mobile station.

[0114] In FIG. 11, at first, a radio mobile station 100 a runs on a lane102 a, and a radio mobile station 100 b runs on a lane 102 b,respectively. Both run at the same speed v1 (=80 km/h). The grouping isdone in accordance with moving speeds of the radio mobile stations 100.For example, it is set such as a group 1 of a speed v1 and a group 2 ofa speed v2 (=100 km/h). Then, a channel ch1 is assigned to the group 1(the radio mobile stations 100 a, 100 b), and a channel ch2 is assignedto the group 2.

[0115] After that, when the radio mobile station 100 b accelerates itsspeed and increases its speed up to the v2, the radio mobile station 100b passes the radio mobile station 100 a ahead. So, the mutualinterference of the channel ch1 may is induced. Thus, in this case, thechannel assigned to the radio mobile station 100 b is changed from ch1to ch2.

[0116] In this way, according to the third radio channel settingexample, it is possible to avoid in advance the situation that the radiomobile stations using the same channel interfere with each other. Inshort, the change of the channel disables the beam patterns of theantenna 92 to intersect with each other, as shown in FIG. 11. Thus, itis possible to protect the interference in the same channel. Moreover,if the speed is conversely decreased, it is possible to similarly changethe channel to thereby protect the interference in the same channel.

[0117] (Fourth Radio Channel Setting Example)

[0118] A fourth radio channel setting example according to the secondembodiment of the present invention will be described below. FIG. 12 isa view explaining this fourth radio channel setting example. The equalor similar symbols are given to the portions equal or similar to thoseof FIGS. 9A and 9B. This fourth setting example is applied to a casethat the running lane of the radio mobile station is changed, in thefirst and second setting examples. Here, let us suppose that the numberof available radio channels is 2, and the grouping is done for eachdifferent two movement lanes of the radio mobile station.

[0119] In FIG. 12, at first, a radio mobile station 104 a runs on a lane106 b at a speed v1 (=80 km/h). Behind the radio mobile station 104 a, aradio mobile station 104 b runs on the same lane 106 b at a speed v2(=100 km/h). The grouping is done in accordance with running lanes ofthe radio mobile stations 104. For example, it is set such as a group 1of a running lane 106 a and a group 2 of the running lane 106 b (theradio mobile stations 104 a, 104 b). Then, a channel ch1 is assigned tothe group 1, and a channel ch2 is assigned to the group 2.

[0120] After that, when the radio mobile station 104 b moves in close tothe radio mobile station 104 a and then the radio mobile station 104 agives the lane to the radio mobile station 104 b, it is necessary tochange the lane of the radio mobile station 104 a. In this case, theradio base station controller 86 controls so as to change the channelassigned to the radio mobile station 104 a from ch1 to ch2.

[0121] In this way, according to the fourth radio channel settingexample, it is possible to avoid the pass or the pursuit between theradio mobile stations to which the same channel is assigned. Thus, it ispossible to protect the beam patterns of the antenna 92 fromintersecting with each other, as shown in FIG. 12. Hence, theinterference in the same channel can be avoided, and the same channelcan be used in a wide range to thereby improve the usage efficiency ofthe frequency.

[0122] (Fifth Radio Channel Setting Example)

[0123] A fifth radio channel setting example according to the secondembodiment of the present invention will be described below. FIG. 13 isa view explaining this fifth radio channel setting example. This fifthradio channel setting example shows the example in which the radio basestation controller detects a moving speed and a position information(for example, a running lane) of the radio mobile station, in the firstto fourth setting examples. The equal or similar symbols are given tothe portions equal or similar to those of FIGS. 9A and 9B.

[0124] In FIG. 13, a radio mobile station 108 recognizes its movingspeed by using a speed meter, a gyro, a GPS, a magnetic sensor and thelike. Also, it recognizes its position information by using a gyro, aGPS, a magnetic sensor, a CCD camera and the like. Then, the radiomobile station 108 uses a channel ch1, and sends the speed informationand the position information as a transmission information “a” through aradio base station 92 to the radio base station controller 86.

[0125] On the other hand, the radio mobile station 108 uses the channelch1, receives a reception information “b” through the radio base station92, and obtains a road traffic information from the radio base stationcontroller 86.

[0126] In this way, in this fifth radio communication system, the radiobase station controller 86 can detect the moving speed and the positioninformation of the radio mobile station 108 through the radio basestation 92, and can easily carry out the assignment of the channel.

[0127] (Sixth Radio Channel Setting Example)

[0128] A sixth radio channel setting example according to the secondembodiment of the present invention will be described below. FIG. 14 isa view explaining this sixth radio channel setting example. This sixthsetting example is applied to an example in which a plurality of radiomobile stations have the moving speeds different from each other. Theequal or similar symbols are given to the portions equal or similar tothose of FIGS. 9A and 9B

[0129] In FIG. 14, a plurality of radio mobile stations 112 a, 112 b,112 c, 112 d and 112 e run on a lane 114 a at the same speed v1(relatively slow speed). Also, a radio mobile station 112 f runs on alane 114 b at a speed v2 (relatively fast speed). Actually, anoccurrence of an accident, a position close to an interchange and thelike cause a traffic jam to be induced on the lane 114 a. Thus, thisfact makes the speeds of the radio mobile stations 112 a, 112 b, 112 c,112 d and 112 e slower. On the other hand, the traffic jam is notinduced on the lane 114 b. So, the radio mobile station 112 f smoothlymoves, and its speed is fast.

[0130] On the lane 114 b in which the traffic jam is not induced, themoving speed of the radio mobile station 112 f is fast to thereby make afrequency of a hand-over process between the radio base stations 88higher. On the other hand, on the lane 114 a in which the traffic jam isinduced, a distance between the cars becomes short to thereby increasethe number of radio mobile stations 112 managed by one radio basestation 88. However, the frequency of the hand-over process is dropped.Moreover, the changes in the position information and the speedinformation given by the radio mobile station 112 and the road trafficinformation given by the radio base station 88 are gentle. For thisreason, when the radio mobile station 112 is stopped or the traffic jamis induced, a temporal interval to communicate with the radio basestation 88 can be wider as compared with the case of the fast movingspeed. Hence, it is possible to further carry out the re-use of the samechannel and also possible to improve the usage efficiency of thefrequency.

[0131] In the first and second embodiments of the present invention, inorder that the radio base station controller 86 controls the hand-overprocess of the radio mobile station 112, the beam pattern generated bythe antenna 92 of each radio base station 88 must follow the radiomobile station 112. Thus, it is necessary to transmit and receive someradio signal between the radio base station 88 and the radio mobilestation 112 at all times. Here, it is necessary to carry out thistransmission/reception at least one time within a beam area in which onebeam is generated. This is because as described in the first embodimentof the present invention, the radio base station controller 86 receivesthe transmission signal of the radio mobile station 112 to therebyselect the optimal transmission beam pattern. Hence, the radio mobilestation 112 must transmit some transmission signal through the radiobase station 88 to the radio base station controller 86 even if there isno information to be sent. In this case, the transmission signal to theradio base station controller 86 from the radio mobile station 112 maybe basically any type if it is a signal that can uniquely point out theradio mobile station 112. For example, it is enough to use an emptypacket having no data. This is because a packet enables the radio mobilestation 112 to be pointed out from its header information.

[0132] Its transmission period is established on the basis of the movingspeed of the radio mobile station 112. Actually, if the radio mobilestation 112 moves at a high speed, a switching frequency of the beampattern is high. Thus, it is enough to make the transmission periodshorter. Conversely, if it moves at a low speed, the switching frequencyis low. Hence, it is enough to make the transmission period longer.Accordingly, the radio base station controller 86 can generate theoptimal transmission beam pattern without using an external sensor andthe like, and control the radio mobile station process of the radiomobile station 112 within the management area.

[0133] (Third Embodiment)

[0134] A third embodiment of the present invention will be describedbelow. The first and second embodiments are the embodiment with regardto the hand-over process between the radio base stations within the areamanaged by one radio base station controller. However, this thirdembodiment is an embodiment with regard to a hand-over process betweentwo different radio base station controllers. FIG. 15 is a view showinga configuration of a radio communication system according to the thirdembodiment of the present invention. In the radio communication systemaccording to the third embodiment of the present invention, similarly tothe first embodiment, a plurality of areas (cells) managed by each basestation are gathered to constitute the entire service area in the mobilecommunication network. Also, in FIG. 15, the explanation is done underthe assumption that the number of base stations managed by one basestation controller is 3, for the purpose of simple illustration.

[0135] In the radio communication system according to the thirdembodiment of the present invention of FIG. 15, a radio base stationcontroller 116 k−1 is connected to three radio base stations 118 i−1,118 i and 118 i+1, and controls them. Each radio base station 118generates a plurality of beam patterns, and has antennas 120 i−1, 120 iand 120 i+1 through which a radio communication with a radio mobilestation (not shown) can be done respectively. Each radio base station118 carries out a radio communication with a radio mobile station withinthe managing base station areas 122 i−1, 122 i and 122 i+1, under thecontrol of the beam pattern of each antenna 120. In short, the radiobase station controller 116 k−1 manages an entire area 124 k−1 composedof the plurality of base station areas 122.

[0136] Similarly, the radio base station controller 116 k is connectedto three radio base stations 126 i−1, 126 i and 126 i+1, and controlsthem. Each radio base station 126 generates a plurality of beampatterns, and has antennas 128 i−1, 128 i and 128 i+1 through which aradio communication with a radio mobile station (not shown) can be donerespectively. Each radio base station 126 carries out a radiocommunication with a radio mobile station within the managing basestation areas 130 i−1, 130 i and 130 i+1, under the control of the beampattern of each antenna 128. Namely, the radio base station controller116 k manages an entire area 124 k composed of the plurality of basestation areas 130.

[0137] Although not shown, the radio base station controller 116 k+1 issimilarly connected to three radio base stations, and controls an entirearea 124 k+1 (not shown). Moreover, the radio base station controllers116 k−1, 116 k and 116 k+1 are connected through a network 132 to eachother.

[0138] The third embodiment of the present invention especially targetsthe inter-lane communication in the high road traffic system (ITS),similarly to the first and second embodiments. As exemplified in FIG.15, an incoming road 136, an outgoing road 138, an interchange 140 andthe like are connected to a straight road 134 on which the radio mobilestation is running. The radio base station 118 connected to each radiobase station controller 116 k needs to cover all of them.

[0139] The feature of the third embodiment lies in a mechanism that aboundary between cover areas of each radio base station controller 116is arranged on a straight road. For example, in a case of FIG. 15, aboundary A-A′ between a cover area 124 k−1 of the radio base stationcontroller 116 k−1 and a cover area 124 k of the radio base stationcontroller 116 k is arranged on the straight line 134. Such anarrangement enables the control of the hand-over process between theradio base station controllers 116 which is the most complex to besimplified.

[0140] That is, the base station areas 122, 130 of the radio basestation 118 which are the movement destinations of a radio mobilestation can be uniquely determined by arranging this boundary A-A′ onthe straight line 134. Thus, the radio base stations 118, 126 of thehand-over destination can be pointed out to thereby simplify the controlof the hand-over process. Usually, the establishment of a communicationline must be again done from the beginning in many cases, in thehand-over process between the radio base station controllers 116. Insuch a case, it takes a long time to carry out the hand-over. So, theremay be a possibility of a stop of a communication for a long time. Inthe inter-lane communication, an automatic drive of a mobile body isconsidered as a future subject. If it takes a long time to carry out thehand-over, there may be a possibility that this brings about a fatalproblem. According to the third embodiment of the present invention,such a problem can be solved by arranging the boundary between the coverareas 124 of the radio base station controllers 116 on the straight line134. Hence, this is very effective in view of improving the reliabilityof the communication and the safety.

[0141] According to the first and second embodiments, it is easy tocontrol the beam patterns within the plurality of radio base stations118, 126 managed by one radio base station controller 116. So, thehand-over between the radio base stations 118, 126 can be relativelyeasily done at a high reliability. Thus, as for the incoming road 136,the outgoing road 138, the interchange 140 and the like, the respectiveradio base stations 118, 126 are arranged such that they can be coveredby the areas of the radio base stations 118, 126 controlled (connected)by one radio base station controller 116. Hence, the radio communicationsystem as a whole can attain the communication having the higherreliability.

[0142] As mentioned above, according to the third embodiment of thepresent invention, the hand-over destination (movement destination) ofthe radio mobile station between the radio base station controllers canbe pointed out to thereby make the control of the hand-over process inthe radio mobile station easier.

[0143] (Fourth Embodiment)

[0144] A fourth embodiment of the present invention will be describedbelow. This fourth embodiment shows the actual control example of thehand-over process between the radio base station controllers, in thethird embodiment. FIG. 16 is a view showing a configuration of a radiocommunication system according to the fourth embodiment of the presentinvention. In the radio communication system according to the fourthembodiment of the present invention, similarly to the first to fourthembodiments, the plurality of areas (cells) managed by each base stationare gathered to constitute the entire service area in the mobilecommunication network.

[0145] In the radio communication system according to the fourthembodiment of the present invention, a first radio base stationcontroller 142 is connected to N radio base stations BS (G1,1), BS(G1,2), BS (G1,3), . . . , BS(G1,N−2),BS(G1,N−1) and BS (G1,N), andcontrols them. The first radio base station controller 142 uses a firstradio base station group G1 composed of the N radio base stations BS(G1,1) to BS (G1,N) and gives an ITS service to a part on a road 144.Similarly, a second radio base station controller 146 is connected to Mradio base stations BS (G2,1), BS (G2,2), BS (G2,3), . . . , BS(G2,M−2), BS (G2,M−1) and BS (G2,M), and controls them. The second radiobase station controller 146 uses a second radio base station group G2composed of the M radio base stations BS (G2,1) to BS (G2,M) and givesan ITS service to another part on the road 144. The first radio basestation controller 142 and the second radio base station controller 146can send and receive a communication call to and from a radio mobilestation 150 through a network 148. In FIG. 6, it is assumed that theradio mobile station 150 moves in a direction from the first radio basestation group G1 to the second radio base station group G2, on the road144.

[0146] The first and second radio base station controllers 142, 146 havea function of sequentially monitoring a radio base station communicatingwith the radio mobile station 150, in the first and second radio basestation groups G1, G2 managed by the respective radio base stationcontrollers 142, 146. Moreover, they control the hand-over processesbetween the radio base stations within the radio base station groupsmanaged by the respective radio base station controllers 142, 146,similarly to the first and second embodiments.

[0147] The operation of the fourth embodiment of the present inventionwill be described below with reference to FIG. 17. FIG. 17 is aflowchart showing a procedure of the hand-over process according to thefourth embodiment of the present invention. As shown in FIG. 17, thefirst radio base station controller 142 detects a start of acommunication between the radio mobile station 150 and a radio basestation BS (G1,Kc) (Kc≦N) serving as a start point of the hand-overprocess, in conjunction with a movement of the radio mobile station 150(Step S301). Here, the radio base station BS (G1,Kc) is the radio basestation within the radio base station group G1 close to a boundary(hereafter, referred to as a control boundary) between the radio basestation group G1 controlled by the first radio base station controller142 and the radio base station group G2 controlled by the second radiobase station controller. Actually, it corresponds to a radio basestation BS (G1,N) that is the closest to the control boundary, or aradio base station BS (G1,K) (K<1) in the vicinity of the controlboundary, such as a radio base station BS (G1,N−1) or BS (G1,N−2)adjacent to the radio base station BS (G1,N), in a case of FIG. 16.

[0148] The first radio base station controller 142, when detecting thestart of the communication between the radio mobile station 150 and theradio base station BS (G1,Kc), sends a control signal (hand-over requestsignal) requesting a start of a hand-over process operation through theradio base station BS (G1,Kc) to the radio mobile station 150 (StepS302).

[0149] The first radio base station controller 142 transfers aninformation sent to the radio mobile station 150 from the radio basestation BS (G1,Kc), through the network 148 to the second radio basestation controller 146 (Step S303).

[0150] The second radio base station controller 146 transmits a signalincluding the transferred information, through a radio base station BS(G2,Lc) (Lc≧1) close to the control boundary, to the radio mobilestation 150. This transmission is done in accordance with a command tothe second radio base station controller 146 from the first radio basestation controller 142 (Step S304). Here, the radio base station BS(G2,Lc) is the radio base station within the radio base station groupG2, which is close to the control boundary. Actually, it corresponds toa radio base station BS (G2,1) that is the closest to the controlboundary, or a radio base station BS (G1,L) (L>1) in the vicinity of thecontrol boundary, such as a radio base station BS (G2,2) or BS (G2,3)adjacent to the radio base station BS (G2,1), in a case of FIG. 16.

[0151] The radio mobile station 150 starting the hand-over processstarts receiving two signals including the same information, which aresent from both the radio base station groups G1, G2 (Step S305).

[0152] The radio mobile station 150 receiving the two signals comparestheir reception states at a certain cycle. It continues the comparison,as long as the reception state of the signal from the radio base stationgroup G1 (the hand-over source) is better (Step S306).

[0153] Then, it stops receiving the signal from the radio base stationgroup G1 when the reception state of the signal from the radio basestation group G2 (the hand-over destination) becomes better, inconjunction with the movement of the radio mobile station 150, andcompletes the hand-over process (Step S307). Two processes as describedbelow may be considered as the actual processes after the radio mobilestation 150 stops receiving the signal from the radio base station groupG1.

[0154] (1) The radio mobile station 150 stops receiving the signal fromthe radio base station group G1, and reports the stop of the processthrough the radio base station group G2 to the second radio base stationcontroller 146. The second radio base station controller 146 reports itsfact to the first radio base station controller 142. The first radiobase station controller 142 receiving its report stops the transmissionto the radio mobile station 150. This first process has the effect ofprotecting an error operation such as an erroneous stop of thetransmission from the radio base station group G1 of the first radiobase station controller 142, if the moving speed of the radio mobilestation 150 is very slow because of the traffic jam and the like, and avariation in a reception strength of the signal to the radio basestation group G1 from the radio mobile station 150 is not evident.

[0155] (2) The first radio base station controller 142 detects thereception strength of the transmission signal to the radio base stationgroup G1 from the radio mobile station 150, and stops the transmissionwhen a sufficient quality is not obtained. Then, thetransmission/reception control to the radio mobile station 150 is turnedover to the second radio base station controller 146. According to thissecond process, the signal between the radio base station controllersand another control signal can be reduced as compared with the firstprocess.

[0156] Typically, in the TDMA mobile communication, the comparison of areception quality such as a reception field strength and the like iscarried out in a plurality of slots. The hand-over is carried out bydetecting the fact that the reception quality from the radio basestation communicated until that time is inferior to a reception qualityfrom another radio base station. In this case, an operation for thehand-over control between the radio base station controllers is actuallycarried out from the judgment of the reception quality. So, the timenecessary for the completion of the hand-over becomes very long. Forthis reason, in order to carry out the hand-over without the qualitydeterioration even in the radio mobile station moving at a high speed,it is necessary to reserve a very large overlap area between two basestation areas close to the control boundary.

[0157] On the contrary, if the radio mobile station moves towards aconstant direction without any branch such as an expressway, it ispossible to predict in advance a positional range of an occurrence ofthe hand-over between the radio base station controllers such as thecontrol boundary or the like. The feature of the fourth embodiment ofthe present invention lies in a mechanism that in the positional rangewhere this predictable hand-over is induced, an information to betransmitted is shared in advance between the radio base stationcontrollers adjacent to each other, and it is simultaneously transmittedto the same radio mobile station. This feature enables the reduction inthe overlap area between the radio base station controllers, even if themoving speed is very fast such as the expressway, as compared with amethod depending on only the comparison of the reception quality such asthe reception field strength in the case of the hand-over in the TDMAmobile communication. Moreover, this provides a merit of largelyreducing a possibility of an interruption of a communication and alsoshortening a control time.

[0158] In the fourth embodiment of the present invention, the setting ofthe radio channel when both the radio base station groups G1, G2transmit signals including the same information may be considered asfollows. At first, it may be considered to basically transmit thesignals at the same frequency and obtain a diversity effect in a smallfrequency offset, if using a multi-office simultaneity communication(for example, noted in “Foundation of Mobile Communication” reported byShinshi Okumura, and announced in Electronic Information CommunicationSociety, p.180, 1986). This case does not require a new assignment ofanother communication slot. So, it is possible to obtain an effect ofimproving a usage efficiency of a frequency and simplifying a control.Also, the transmissions through the same slot may be considered if a TDMslot synchronization can be reserved between the first and second radiobase station controllers 142, 146. In addition, it may be consideredthat another TDM slot is used in a case of TDM, and a receiving sidereceives a plurality of TDM slots. Moreover, it may be considered thatanother diffusion code is used in a case of CDM, and a receiving sideperforms an inverse diffusion on a plurality of codes.

[0159] As described in the second embodiment, the first radio basestation controller 142 can have the function of obtaining the speedinformation of the radio mobile station 150. Thus, in the fourthembodiment of the present invention, the first radio base stationcontroller 142 can properly select a position of the radio base stationBS (G1,Kc) from the radio base station group G1, in accordance with themoving speed of the radio mobile station 150, and thereby improve thereliability of the hand-over process, and accordingly reduce theconsumptive electric power.

[0160] That is, if the speed of the radio mobile station 150 is fast,the radio base station BS (G1,Kc) is moved to a direction away from thecontrol boundary between the first and second radio base stationcontrollers 142, 146. Accordingly, a time required for the radio mobilestation 150 to reach the control boundary can be made longer. Thus, thehand-over process can be completely ended within the time. Hence, it ispossible to protect the radio mobile station 150, in which the hand-overis not still ended, from coming into the area of the adjacent radio basestation group G2.

[0161] On the contrary, for example, in a condition that an occurrenceof the traffic jam of the radio mobile stations (cars) causes the speedto be very slow or causes the radio mobile station 150 to be stopped, itis enough to shift the radio base station BS (G1,Kc) to a directioncloser to the control boundary. This reason is as follows. That is, ifthe radio base station BS (G1,Kc) is far away from the control boundaryin the case of the slow speed of the radio mobile station 150, thecontrol is started earlier than a timing when the hand-over controlshould be actually started. Thus, although the radio mobile station 150does not still reach the area of the radio base station group G2, atransmission signal for the hand-over is uselessly transmitted from theside of the radio base station group G2. Also, the reception operationsin a plurality of base stations for the hand-over are uselessly carriedout even in the radio mobile station 150, which thereby brings about theincrease in the consumptive electric power. Especially, the number ofradio mobile stations 150 managed by one radio base station is verylarge in a case of the traffic jam, the position near the interchangeand the like. Hence, a traffic density becomes much denser due to thecommunication with regard to the hand-over. Hence, a scrap rate of apacket in which a congestion is liable to be induced becomes large tothereby deteriorate the communication situation.

[0162] In the fourth embodiment of the present invention, the respectiveradio base stations in the radio base station groups G1, G2 are arrangedin a certain interval “r” along the road 144, on the straight portion ofthe road 144. Here, if an interval “r” between a radio base station BS(G1,N) that is the closest to the control boundary and a radio basestation BS (G2,1) is made shorter, it is possible to widen a range inwhich a base station area of the radio base station BS (G1,N) and a basestation area of the radio base station BS (G2,1) overlaps with eachother, even if the similar antenna and transmission electric power areused in the respective radio base stations. Thus, it is possible toobtain an effect of reducing a probability that a communication with aninfrastructure side is interrupted within the time required for theradio mobile station 150 to carry out the hand-over.

[0163] If a plurality of modulation manners having differenttransmission rates are permitted at a time of the transmission/receptionin the first and second radio base station controllers 142, 146according to the fourth embodiment of the present invention, it isenough to basically select the modulation manner having the lowertransmission rate at the time of the transmission/reception in thehand-over operation. Accordingly, it is possible to earlier obtain a bitsynchronization of an accuracy necessary for the communication betweenthe radio mobile station 150 and a radio base station belonging to theradio base station group G2, as compared with a case of the highertransmission rate. Thus, it is possible to obtain an effect ofshortening a time necessary for the hand-over operation. Similarly, if aplurality of coding manners having different error correction codes arepermitted, it is enough to basically select the manner having a strongerdurability for a transmission error. Of course, it is not alwaysnecessary to select a modulation manner having the lowest transmissionrate or a coding manner having the strongest durability for thetransmission error. The selection of the modulation manner or the codingmanner should be done flexibly in accordance with the moving speed ofthe radio mobile station 150. For example, with regard to the radiomobile station 150 moving at a high speed, it is enough to select themodulation manner having the lowest transmission rate or the codingmanner having the strongest durability for the transmission error. Onthe other hand, with regard to the radio mobile station 150 moving at alow speed, it is not always necessary to select the modulation mannerhaving the lowest transmission rate or the coding manner having thestrongest durability for the transmission error

[0164] By the way, as the plurality of modulation manners having thedifferent transmission rates, there may be, for example, a case thatonly baud rates are different although signal point transitions areequal, a case that the signal point transitions are different althoughthe baud rates are equal (for example, QPSK and 16 QAM) and a case thatboth the baud rate and the signal point transition are changed.

[0165] Also, as the plurality of modulation manners, there may be: acombination of 1024 QAM, 256 QAM, 16 QAM and QPSK, or a combinationusing at least two of them; 1024 QAM-OFDM, 256 QAM-OFDM, 16 QAM-OFDM andQPSK-OFDM, or a combination using at least two of them; and acombination of 16 PSK, 8 PSK, QPSK and BPSK, or a combination using atleast two of them. Any of the above-mentioned combinations enable themodulation in a single modulating circuit or a demodulation in a singlemodulating circuit. Thus, this has a merit of easily configuring atransmitter or a receiver. Also, it may be considered that a combinationof FSK and QPSK used in the ITS field in relatively many cases has amerit of using an existing transmission/reception circuit in the field.

[0166] By the way, when the multi-office simultaneity transmission isdone at a time of the hand-over as mentioned above, there is a meritthat a lower baud rate is desirable in order to protect a mutualinterference and obtain a diversity gain as much as possible.

[0167] As mentioned above, according to the fourth embodiment of thepresent invention, the communication can be smoothly switched from thefirst radio base station controller of the radio mobile station to thesecond radio base station controller. Thus, it is possible to easilycontrol the hand-over process. Moreover, the hand-over process of theradio mobile station between the radio base station controllers can bemade effective.

[0168] According to the present invention, it is possible to provide aradio communication system which can make the control of the hand-overprocess easier and improve the reliability of the communication.

[0169] According to the present invention, it is possible to provide aradio communication system which can make the control of the hand-overprocess easier and make the communication effective.

[0170] Various modifications will become possible for those skilled inthe art after receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. A radio communication system comprising: (a) atleast one mobile station; (b) a plurality of base stations configured togenerate a plurality of beam patterns; and (c) a base station controllerwhich is connected to the plurality of base stations, and then assigns afixed channel to each mobile station, controls the beam patterns of thebase stations and accordingly carries out a radio communication with themobile station, the base station controller having a device which whencarrying out a transmission and a reception to and from a differentmobile station to which the same channel is assigned, controls the beampatterns so that the channels do not interfere with each other.
 2. Aradio communication system of claim 1 , wherein the mobile station is amobile station running on a road, and at least a part of the pluralityof base stations are arranged along the road.
 3. A radio base stationcontroller which is connected to a plurality of base stations configuredto generate a plurality of beam patterns, and then controls an antennathat is installed in each of the base stations and composed of aplurality of antenna devices, and accordingly carries out a radiocommunication with a mobile station, the radio base station controllercomprising: (a) an antenna controller configured to control the antennain each of the base stations; and (b) at least onemodulating/demodulating device configured to modulate and demodulate asignal which is transmitted to and received from the mobile station. 4.A radio base station controller of claim 3 , wherein the antennacontroller comprises: a selector configured to select at least oneantenna device from the plurality of base stations; and a setterconfigured to set a weight of the selected antenna device.
 5. A radiobase station controller of claim 4 , wherein the setter has a deviceconfigured to determine the weight of the antenna device so that when atransmission or a reception is carried out to or from a different mobilestation to which the same channel is assigned.
 6. A radio base stationcontroller of claim 4 , wherein the antenna controller further has ameasuring device configured to measure respective reception strengths ofthe respective antenna devices in the plurality of base stations.
 7. Aradio base station controller of claim 3 , wherein the mobile station isa mobile station running on a road, and at least a part of the pluralityof base stations are arranged along the road.
 8. A radio base stationcontroller which is connected to a plurality of base stations arrangedalong a road, and then controls the plurality of base stations, andaccordingly carries out a radio communication with at least one mobilestation running on the road, the radio station controller comprising:(a) a device configured to assign the same channel to each mobilestation of the same speed or the same lane; (b) a device configured todetect at least one of the speed and the lane of the mobile station; and(c) a device which when the speed or the lane of the mobile station ischanged, changes an assignment channel, in accordance with a speed or alane after the change.
 9. A radio base station controller of claim 8 ,wherein a communication interval is changed depending on the change ofthe speed of the mobile station.
 10. A radio mobile station which isconnected to a plurality of base stations configured to generate aplurality of beam patterns, and then carries out a radio communicationwith a base station controller that can control an antenna installed ineach of the base stations and composed of a plurality of antennadevices, wherein the radio mobile station transmits a signal includingat least information to identify the radio mobile station, even if thereis not a signal to be transmitted to the base station controller.
 11. Aradio base station controller which is connected to a plurality of basestations arranged along a road, and then controls the plurality of basestations and accordingly carries out a radio communication with at leastone mobile station running on the road, wherein a boundary between radiobase station controllers adjacent to each other is positioned in aportion in which a movement destination of the mobile station on theroad can be pointed out.
 12. A radio communication system comprising:(a) at least one mobile station having a device configured to select,from a plurality of same reception signals, a reception signal in whicha reception state is better; (b) a first base station controller havinga device configured to detect a start of a communication between apredetermined first base station and a mobile station, a deviceconfigured to request a hand-over process to the mobile station, and adevice configured to transfer a transmission signal to the mobilestation to a base station controller of a hand-over destination of themobile station, the first base station controller connected to a firstbase station group including the predetermined first base station; and(c) a second base station controller having a device configured totransmit the transmission signal transferred from the first base stationcontroller, through a predetermined second base station to the mobilestation, the second base station controller connected to a second basestation group including the predetermined second base station.
 13. Aradio communication system of claim 12 , wherein the predetermined firstand second base stations are arranged close to a boundary between thefirst and second base station controllers.
 14. A radio communicationsystem of claim 12 , wherein the mobile station is a mobile stationrunning on a road, and at least a part of the first and second basestation groups including the predetermined first and second basestations is positioned in a portion in which a movement destination ofthe mobile station on the road can be pointed out.
 15. A radiocommunication system of claim 14 , wherein the first base stationcontroller further comprises: a device configured to detect a speed ofthe mobile station; and a device configured to change the predeterminedfirst base station, in accordance with the detected speed.
 16. A radiocommunication system of claim 14 , wherein the first and second basestation groups arranged along the road are arranged in a predeterminedinterval, and an interval between a first base station and a second basestation which are the closest to each other is shorter than thepredetermined interval.
 17. A radio communication system of claim 14 ,wherein the first and second base station controllers select an optimaltransmission rate and error correction code in accordance with a speedof the mobile station when performing a hand-over process on the mobilestation, and then carry out a transmission and a reception to and fromthe mobile station.
 18. A radio communication method comprising thesteps of: (a) detecting a start of a communication between apredetermined first base station connected to a first base stationcontroller and a mobile station running on a road; (b) requesting ahand-over process to the mobile station; (c) transferring to a secondbase station controller, a signal to be transferred through thepredetermined first base station to the mobile station; (d) transmittingthe signal to the mobile station through a predetermined second basestation connected to the second base station controller; and (e)selecting a signal in which a reception state is better, from twosignals received by the mobile station.
 19. A radio communication methodof claim 18 , wherein the predetermined first and second base stationsare arranged close to a boundary between the first and second basestation controllers.
 20. A radio communication method of claim 19 ,wherein the first base station controller is connected to a first basestation group including the predetermined first base station, the secondbase station controller is connected to a second base station groupincluding the predetermined second base station, and at least a part ofthe first and second base station groups including the predeterminedfirst and second base stations is arranged along a portion in which amovement destination of the mobile station on the road can be pointedout.